1. Field of the invention
The present invention relates to an automatic oil pump for lubricating production machinery, and more particularly, to a circuit for monitoring the output pressure of an automatic oil pump and for controlling the timing sequence of the oil pump in accordance with the output pressure.
2. Description of the Background
Tooling and production machinery generally operate with rotary or sliding parts making frictional contact. The performance and life span of such machinery largely depends on lubrication of the rotary and sliding parts.
It is well-known that automatic oil pumps operating according to a set timing sequence are more efficient and reliable than manual lubrication. However, most machinery performs many operations involving different loading conditions. Since different load conditions on the machinery necessitate a longer or shorter pumping sequence by the automatic oil pump, conventional automatic oil pumps operate in accordance with a variable timing sequence.
The variable timing sequence may be controlled manually. However, this requires repeated adjustment of the timing sequence by the operator. Moreover, the operator is unable to detect clogged or damaged internal pump filters or parts, and damage to the machinery may result.
The timing sequence may also be varied automatically. This is preferable because operator interface is minimized. Timing controls which automatically vary the timing sequence preferably operate according to a dual pumping cycle. That is, the timing sequence is controlled by two independent timers. A first adjustable timer controls the frequency at which the intermittent oil pump begins to inject oil. A second adjustable timer controls the length of time during which oil is pumped. However, in the prior art adjustable-cycle automatic oil pumps, if the second timer is set to pump oil for too long the machinery will become saturated at a peak injection pressure. Nevertheless, the pump motor will continue to operate and energy will be wasted. If the timer is set to pump oil for too short a time the proper pressure will not be achieved and insufficient oil will be delivered. In addition, the timing control circuit will be unable to detect a malfunctioning oil pump, and power will be applied to the pump motor according to the timing sequence despite the problem.
U.S. Pat. No. 3,976,989 issued to Smith proposes a partial solution to the problem. Smith '989 discloses a timing circuit employing a pressure sensitive switch and a watchdog timer for monitoring the oil pump output. As soon as pumping begins at a normal flow-rate, the pressure of the flow closes the pressure-sensitive switch. The switch in turn activates the watchdog timer to keep track of the length of time during which pumping continues. If pumping continues for too long an interval, the timer will activate an alarm. Likewise, if the pump is broken and cannot achieve the normal flow-rate pressure, an alarm will sound. The timeout alarms are an important improvement over the prior art, however, they are the sole function of the Smith '989 device. The Smith '989 device only monitors the pump. It does not control it. Moreover, the Smith '989 device only insures that the pump attains the proper output pressure for the proper length of time. It does not insure that the pump achieves saturation pressure within a predetermined time interval.